Although power utilities supply line power to customers of the utilities at a nominal voltage, the actual line voltage varies about the nominal value. Over a large number of customer facilities, the occasional overvoltage represents a significant increase in consumption to the utility. It is therefore known to provide a voltage regulation system associated with a facility that tracks the line voltage from the utility and automatically steps the voltage down to maintain the power supplied to the facility at a voltage value that is closer to the nominal target value.
For example, U.S. Pat. No. 6,066,945 discloses an electric power saving transformer for three-phase current with an automatic voltage transferring device. The device automatically adjusts an output voltage within a predetermined range even when an input voltage is increased or decreased beyond a predetermined range.
The AVR-Harmonizer, offered by Legend Power Systems Inc. of Burnaby, British Columbia, is an autotransformer having a series of taps on the secondary enabling the adjusting of the output voltage of the transformer. The AVR-Harmonizer is placed in series with the line power supply to a building such that on-the-fly selection of individual taps regulates the voltage supplied to the building to within a narrower range than is typically supplied by the power utility. The tap selection is automatically implemented electronically.
Whenever any part of the device is to be replaced, it is necessary to interrupt the supply of power to the facility, resulting in considerable inconvenience if done frequently. The magnetic components of a regulator such as the windings can typically be expected to last 30 years before requiring replacement. On the other hand, the electronic package might require replacement every 10 years or so, and repair or replacement of components from time to time.
It is known to provide line power conditioning and power back-up equipment (particularly UPS's) that include a manual bypass switch to enable the removal and maintenance of the equipment or components thereof. It is also known to provide such systems in conjunction with step-wise tap switching regulators. Examples of this approach are disclosed or discussed in the following publications:                http://news.thomasnet.com/fullstory/539029        http://www.trafficcontrolcorp.com/Product%20Cuts/Tech%20Power_ME%20XL.pdf        http://books.google.ca/books?id=kb7BJNwt6fcC&pg=PA376&lpg=PA376&dq=%22manual+bypass+switch%22&source=web&ots=5BdG-GC_Vl&sig=DZHbd_zfMJWFZabs57qmlEaVAT0&hl=en        http://books.google.ca/books?id=qyHOFnUfCQMC&pg=PA817&lpg=PA817&dq=%22manual+bypass+switch %22+removal+conditioner&source=web&ots=TmKXm4t8d9&sig=YnZCcp7XNai_gZBRj2dSJbjV8oM&hl=en        http://www.solidstatecontrolsinc.com/techhpapers/papers/upsindustrial.html        
Such approaches allow removal of the UPS from the lines without requiring interruption of the power supply to the facility.